In accordance with ASTM definitions, masonry cement is defined as a hydraulic cement for use in mortars for masonry construction, containing one or more of the following materials: Portland cement, Portland blast-furnace slag cement, Portland-pozzolan cement, natural cement, slag cement, or hydraulic lime; and in addition usually containing one or more materials such as hydrated lime, limestone, chalk, calcareous shell, talc, slag, or clay, as prepared for this purpose. The present physical requirements for type-S mortars to meet ASTM C91 specifications are as follows:
Compressive strength (average of 3 cubes): The compressive strength of mortar cubes, composed of 1 part cement and 3 parts graded standard sand by volume, prepared and tested in accordance with this specification shall be equal to or higher than the values specified for the ages indicated below:
______________________________________ 7 days, psi 500 (MPa) (3.45) 28 days, psi 900 (MPa) (6.21) ______________________________________
Air content of mortar, prepared and tested in accordance with requirements of this specification:
______________________________________ Max. volume 22% Min. volume 12% Water retention, flow after 70% suction, of original flow ______________________________________
To achieve these test results, mortars are prepared from the masonry cement of the present invention by proportioning the masonry cement to contain 188 pounds of cement, 50 pounds of high grade limestone and 720 pounds of sand. The sand shall consist of 80 pounds of graded standard sand ASTM C-91. The quantity of water, measured in milliliters shall be such as to produce a flow of 110.+-.5 as determined by the ASTM flow table.
A typical prior art masonry cement contains approximately 188 pounds of Portland cement, 50 pounds high grade limestone and other components, such as an air entraining agent. Typically, masonry cements are manufactured by using a steel ball grinder to grind the limestone with the other components for admixture with the Portland cement. These prior art masonry cements require a relatively high percentage of limestone as a plasticizer to meet ASTM specifications for masonry cements. ASTM specifications for air content in a masonry cement provide for a maximum of 18% by volume to provide void spaces in the masonry cement for expansion of freezing moisture.
The use of a substantial quantity of limestone as a plasticizer in prior art masonry cements creates two significant problems. First, the substantial quantities of limestone necessary to provide sufficient plasticity to the masonry cement reduces the compressive strength of the cement. Second, the limestone must be crushed in a grinder together with other components, such as a polyglycol as a grinding aid, fatty acids as an air entraining agent, and a sucrose solution as a setting agent, to provide a slurry for admixture with the Portland cement. The grinder must be carefully cleaned after each batch so that the masonry cement can be manufactured as a consistent, precise composition. Further, if the masonry cement composition is to be changed between batches, the grinder must be completely cleaned after each batch to make sure that the masonry cement being manufactured meets the ASTM specification for the particular type of masonry cement since it may be prohibitive for a particular type of masonry cement to include a component of the masonry cement previously included in the last limestone grinding batch.
Others have used diatomite, diatomaceous earth, bentonite or hydrous silicates of alumina as a thickening agent in a concrete or mortar generally in an amount of about 2% by weight or less of the cement composition, as disclosed particularly in the Cross Pat. Nos. 1,854,180 and 1,943,584 and, additionally as disclosed in the following U.S. patents:
______________________________________ 1,584,579 2,356,214 2,585,366 1,795,011 2,377,491 3,219,112 1,885,731 2,516,342 1,920,358 2,529,841 ______________________________________
Bentonite and diatomaceous earth when added to Portland cement alone, as disclosed in the Cross Pat. Nos. 1,854,180 and 1,943,584, are not sufficient to provide the necessary water retention and air entrainment properties to make the cement useful as a masonry cement. Mortars prepared with Portland cement containing 2% and 4% by weight bentonite and mortars prepared with Portland cement containing 2% and 4% by weight diatomaceous earth were found to have the following values for water retention, insufficient to meet ASTM specifications.
______________________________________ Portland Portland plus 2% plus 4% Portland Portland diato- diato- plus 2% plus 4% maceous maceous bentonite bentonite earth earth ______________________________________ Water 52 54 48 50 Retention (min. 75%) Air Content 11.9 10.7 7.4 6.8 (min. 12%) ______________________________________
Further, the Weber U.S. Pat. No. 2,643,193 discloses an insulating filler composition useful as an aggregate in place of sand for mixture with hard-wall plaster or cement adapted for mixture with Portland cement and containing both diatomaceous earth and colloidal clay. The maximum clay content, however, is less than 4% by weight and the composition is not adapted to be used as a masonry cement since the composition does not meet ASTM specifications.
This assignee's U.S. Pat. No. 4,377,416 discloses a mortar or masonry cement composition containing at least 5% by weight colloidal clay. In accordance with the present invention, it has been found that new and unexpected results are achieved in a mortar cement including Portland cement, about 0.05 to about 0.8% by weight diatomaceous earth; and about 0.5% to 4.0% water-swellable colloidal clay, such as bentonite. Surprisingly, when a masonry cement composition is prepared to contain, for example, 188 pounds of Portland cement, 720 pounds of graded standard sand and about 0.5% to about 4.0% bentonite based on the weight of Portland cement, diatomaceous earth and bentonite clay, thereby replacing the 50 pounds of limestone, the compressive strengths meet ASTM specifications and are about equivalent to the compressive strengths of masonry cements containing 20% to 42% limestone.